1. Field of the Invention
The present invention relates to the design of optical networks. More specifically, the present invention relates to a method and apparatus that performs hierarchical optical switching to facilitate routing of data across an optical network.
2. Related Art
The explosive growth of the Internet has resulted in the vast demand for bandwidth by network operators. Experts predict that the Internet bandwidth demand will continue to grow rapidly by doubling itself every 6-9 months over the next several years. Such large bandwidth demand, coupled with the large bandwidth that optical fibers offer, is driving the wide deployment of optical networks. However, laying optical fibers in the ground is both expensive and time consuming. To meet the ever-growing bandwidth demand, the industry has been quick to embrace a technology that can multiply the transmission capacity of the existing fibers: wavelength-division multiplexing (WDM). With WDM technology, multiple wavelengths, each carrying a stream of bits at very high speed, can be transmitted simultaneously through a single fiber without interfering with one another.
In a short period of a few years, WDM technology has penetrated most of the optical networks, and will continue to be deployed in the future. New advances in the WDM technology has enabled more wavelengths to be available for telecom usage within the optical fiber""s usable spectrum window. At the present time, the number of wavelengths in a typical telecom optical fiber ranges from 8 to 64, while more than one hundred wavelengths in one single fiber are becoming available in the near future.
As the total capacity of the network multiplies with WDM technology, one major challenge that exists for network operators is to effectively manage the increased amounts of bandwidth. Network operators need to deliver end-to-end connectivity at different data rates. The typical data rate on a wavelength is OC-48 (2.488 Gbps) or OC-192 (10 Gbps), with OC-768 (40 Gbps) becoming standard in the near future. However, connection requests from users come with different data rates. According to the widely-accepted Synchronous Optical Network (SONET) standard, connection are named as OC-N, where N indicates the data rate of the connection. Typical values are OC-1 (51.84 Mbps) (also referred to as STS-1), OC-3 (155.52 Mbps), OC-12 (622 Mbps), OC-48, OC-192, and OC-768. Lower-speed connections are grouped together to fill up the bandwidth of an entire wavelength (i.e., by using time-division multiplexing, TDM). Optical switches are used to inter-connect wavelengths and/or lower-speed connections at the network""s switching nodes. These switching nodes perform two main functions: (1) routing connections from upstream nodes to downstream nodes, and (2) initiating and terminating connections to and from the client network elements (such as IP routers, ATM switches, etc.) which requested the connections.
The current art in switching technologies provides two approaches to the construction of an optical switch: an electronic switch fabric and an optical switch fabric. With an electronic switch fabric, the incoming optical signals are demultiplexed to separate out different wavelengths. Each wavelength is then terminated by a receiver that converts the bits from an optical signal to an electrical signal. These streams of bits then feed into an electronic switch fabric, which reads the bit streams from its input ports and routes them to its output ports. Once the streams exit from the electronic switch fabric, they are converted back to optical signals, on different wavelengths, and are multiplexed back together before entering the outgoing fiber. The electronic switch fabric is typically constructed from integrated circuit (IC) switch chips, which are smaller switches themselves (e.g., a 64xc3x9764 switch chip with 2.488 Gbps per port). Such a switching system is also called an optical-electrical-optical (OEO) switch, which means that all the optical signals are first converted to electrical signals, then switched electronically, and finally converted back to optical signals.
An alternative to electronic switch fabric is to use an optical switch fabric. An optical switch fabric can directly switch optical signals using, for example, tilting mirrors. Hence, it can switch a whole wavelength or a group of wavelengths without reading the bits. However, it cannot switch lower-speed connections within a wavelength.
What is needed is an optical switch that has large capacity and capability to switch different bandwidth granularities, both on the wavelength and sub-wavelength level. It also needs to have excellent scalability, i.e., the cost, power consumption, and size of the switch should be maintained at an acceptable level as the capacity of the switch grows larger.
One embodiment of the present invention provides a system that facilitates optical switching. The system starts by receiving a plurality of optical input signals. The system then divides each of the plurality of optical input signals into a plurality of wavebands that can be carried on a single optical fiber, wherein each waveband includes a predetermined subset of the wavelengths in the optical signal. Once the optical input signals have been divided into wavebands, the wavebands are then routed through a waveband switch. After being routed through the waveband switch, the wavebands are combined to form a plurality of optical output signals, where each optical output signal can possibly include wavebands from different optical input signals. Additionally, some of the wavebands can be divided into wavelengths, and the wavelengths can be routed through a wavelength switch or a traffic grooming switch.
In a variation on this embodiment, the optical input signals are divided into wavebands by sending the optical input signals through an Arrayed Waveguide Grating (AWG) device.
In a variation on this embodiment, some of the plurality of wavebands are further divided into a plurality of wavelengths, and the wavelengths are routed through a wavelength switch. Note that some of the wavebands might be routed through the waveband switch, while others are divided into wavelengths and are routed through the wavelength switch.
In a further variation on this embodiment, the wavebands are divided into wavelengths by sending the wavebands through an AWG device.
In a further variation on-this embodiment, the plurality of wavelengths is further divided into a plurality of Time-Division Multiplexing (TDM) signals, and the TDM signals are routed through a switch. Note that some of the wavelengths might be routed through the wavelength switch, while others are divided into TDM signals.
In a variation on this embodiment, some of the plurality of wavebands are further divided into a plurality of wavelengths, and the wavelengths are routed through a TDM traffic grooming switch. Note that some of the wavebands might be routed through the waveband switch, while others are divided into wavelengths and are routed through the TDM traffic grooming switch.
In a variation on this embodiment, a subset of the optical input signals are routed directly to optical output signals without being divided into wavebands.
In a variation on this embodiment, routing of optical signals is performed by a Micro-Electro-Mechanical Systems (MEMS) based optical switch fabric.
In a variation on this embodiment, routing of optical signals is performed by a micro-fluid based optical switch fabric (bubble switch).